def lone_sum(a, b, c):
  if a!=b and a!=c and b!=c:
    return a+b+c
  if a == b and a!=c:
    return(c)
  if a == b == c:
    return(0)
  if a == c and a!=b:
    return b
  if a!=b and a!=c and b == c:
    return a